I've made a few critical updates to my source document since I first posted on Kindle last Wednesday. I thought I read a KDP doc that said I could push revisions to users, and if I know who they are .. I can tell them to delete local copy and redownload for current version.

I've tried that on my own devices (Kindle, Droid, PC) and its not working; I keep getting the older version. Is there something else I need to be doing?

Email kdp-support and ask them to inform buyers that a "corrected version" (I think that's the only language they will use) is available.

The reader must then go to his Archives and download the updated version. I doubt that many will do so. However, it's a nice gesture if not done too often (in which case readers might start to think you publish without careful vetting).